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Methodology and results of the evaluation of alternative short tests applied in inspection and maintenance programmes
Transportation Research Part D 6 (2001) 111±122
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Methodology and results of the evaluation of alternative short tests applied in inspection and maintenance programmes Zissis Samaras *, Ioannis Kitsopanidis 1 Laboratory of Applied Thermodynamics, Department of Mechanical Engineering, Aristotle University, 54006 Thessaloniki, Greece
Abstract The aim of this paper is to present a methodology for the evaluation of the eectiveness of alternative short tests that could be applied in an inspection and maintenance programme. The basis for the evaluation, apart from the environmental bene®ts, is the social and political acceptance that constitutes crucial parameters in the implementation of a short test. The methodology has been applied to a large sample of three way catalyst equipped vehicles representative of the European ¯eet and the eectiveness of 10 alternative short tests has been evaluated. The short tests include transient and steady state (both loaded and unloaded) procedures, as well as the idle test of the current European legislation. The steady state tests ®nd it dicult to identify high emitters, approximately 15% are detected, and as a result the predicted potential for environmental bene®t is less than 5% for all pollutants. The transient tests, on the other hand, seem to be able to identify approximately 70% of gross emitters and therefore the emission reduction potential is predicted to be as high as 20% for all pollutants. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Inspection and maintenance; Short test; Emission reduction potential; Errors of commission; Cut-points; Emission standards
1. Introduction The European exhaust emission regulations for the registration of new vehicles have increased in stringency over the last two decades (Concawe, 1997). These legislative steps, that re¯ect the technological achievements over this period, have not proved to be sucient to achieve the aspirated for emission levels of pollutants from vehicles. The sensitivity of the complex electronic systems of modern cars along with the poor maintenance of in-use vehicles seem to be crucial with
*
Corresponding author. Tel.: +30-31-996014; fax: +30-31-996019. E-mail address: [email protected] (Z. Samaras). 1 Present address: Sloan Automotive Lab, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
1361-9209/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 1 3 6 1 - 9 2 0 9 ( 0 0 ) 0 0 0 1 6 - X
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regard to the high emission levels from vehicles shortly after their certi®cation. The periodic inspection and repair of in-use vehicles, therefore, have merit. The so-called inspection and maintenance (I/M) programmes aim to ensure that motor vehicle emission control systems are functioning properly throughout the lifetime of the vehicle. Such programmes, that have been enacted for the ®rst time in the 1960s in California, have never achieved the predicted emission reductions (Environmental Protection Agency, 1995; Pierson, 1996). An I/M programme can yield eective results only within an appropriate legislative and administrative framework and when the technical parameters are clearly determined. These technical aspects, that can be grouped by the name Ôshort testsÕ, may contribute substantially to the aim of the emissions reduction programme (Samaras, 1997). The methodology described used here attempts to assess the eectiveness of alternative short tests applied to I/M programmes.
2. Methodology A short test can be considered eective only when it yields an acceptable correlation to the certi®cation cycle or a cycle that is representative of actual driving conditions (Pattas and Hassiotis, 1987; Faiz et al., 1996). Fig. 1 presents such a correlation where the emissions of a particular pollutant over a short test (horizontal axis) are correlated to the corresponding emission levels over the certi®cation cycle (vertical axis). Fig. 1 distinguishes six vehicle groups that play a major role in the analysis, divided by policy lines (Samaras, 1997). The ®rst horizontal line corresponds to the vehicle emission standard for
Fig. 1. Basic chart.
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the target pollutants. The second horizontal line is drawn showing a percentage a above the emission standard and aims to distinguish the high (groups 3 and 4) and the very high polluters (groups 5 and 6) according to their emissions over the certi®cation cycle. The vertical line corresponds to the short test cut-point, i.e., the limit for approving vehicles. This line has been drawn so that the short test is as eective as possible. The vehicles belonging to group 1 are Ôlow pollutersÕ since they emit below the standard and pass the short test. Group 6 vehicles are seen as Ôneeding repairÕ since they are high polluters and fail the short test. The greater the number of vehicles in these two groups, the more eective the short test is. The low polluters of group 2 are incorrectly detected by the short test and, therefore, they are called Ôerrors of commissionÕ. The very high polluters of group 5 are called Ôerrors of omissionÕ, since these vehicles are not detected. In most cases, short tests measure more than one pollutant and this complicates the distribution of vehicles into groups. A particular vehicle could be placed in dierent groups for dierent pollutants. In practice, when a vehicle is tested, only two groups are identi®ed: those passing (groups 1, 3 and 5) and those failing the test (groups 2, 4 and 6). This means that when emissions exceed the cut-point at least in one pollutant the vehicle is sent to maintenance. Thus, a vehicle is referred to: · as needing repair, when at least one pollutant lays in group 6; · as error of commission, when at least one pollutant emission lies in group 2, but none in group 6; · as error of omission, when it passes the short test even though it has excessive emissions at least in one pollutant; and · as low polluter, when it passes the short test and emits below the standard for all pollutants. References to vehicle groups do not, therefore, concern particular pollutants, but are made to pollutants as a whole according to the above de®nitions (Fig. 2). The basic concept for evaluating the eectiveness of alternative short tests is to calculate the overall emission reduction achieved for each pollutant, assuming that vehicles that fail the short test (groups 2, 4 and 6) have the same emission levels as low polluters (group 1). The major contribution to this reduction comes from the vehicles needing repair (group 6), while no emission reduction is achieved by errors of commission (group 2). The vehicles laying in group 4 at least in one pollutant, having though no pollutants in groups 2 and 6 are seen as vehicles oering low environmental bene®t, since their average emissions are low compared to the emissions of the vehicles needing repair. The validity of this assumption depends on the value of a and the emission characteristics of the ¯eet. Assuming the malfunction of these vehicles to be minor, and dicult to detect, the methodology does not take into account the environmental bene®ts from these vehicles. On the other hand, it is assumed that all vehicles needing repair emit after maintenance the same levels of pollutants as when new, i.e., it is assumed that they are completely repaired. This assumption is optimistic and, therefore, the emission reduction should be considered as ÔpotentialÕ. The eect of maintenance is believed to be a parameter independent of the short tests and thus should be investigated separately. If i denotes the pollutants, FC the fuel consumption, and j the vehicle groups, three indexes can be de®ned: Nj , the number of vehicles in group j, Pj , the percentage of vehicles tested laying in group j and Eij , the cumulative pollutant i emissions of group j vehicles measured over the certi®cation cycle.
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Fig. 2. Flowchart for separating the vehicles into groups.
Based on the above, the following `derivative' indexes can be de®ned: Eij ; Emission factor : EFij Nj Emission reduction potential : ERPi EFi6 ÿ EFi1 N6 ; ERPi Emission reduction rate potential : ERRPi 100%: Ei
1 2 3
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The parameters that characterise a short test are: · ERRPi : the potential environmental bene®t that can be achieved with respect to pollutant i, when the particular short test is applied in the framework of an I/M programme. ERRP is the equivalent of the parameter identi®cation rate (IDR) introduced in similar evaluations of the Environmental Protection Agency (1995). · P6 : The part of the vehicle ¯eet sent to maintenance, which generates the above mentioned emission reduction. · P2 : The percentage of vehicles wrongly failed by the short test. Since one objective of an I/M programme is the generation of high environmental bene®t at low cost and with minor inconvenience, ERRPi should be as high as possible with low P6 and P2 values. P6 and P2 should be within the range of political and social acceptance in terms of the costs of maintenance of the programme and legal protection. This does not take into account errors of omission (P5 ), that indirectly indicate a loss of environmental bene®t. Since the environmental gain is directly accounted for by ERRP, P5 provides no additional information. The methodology can be applied to all pollutants for which emission standards exist; i.e., CO, HC and NOx for gasoline vehicles. Direct application of the approach to CO2 emissions and FC is not possible, due to the absence of legal standards. However, the potential reductions of CO2 and FC may be evaluated from Eqs. (1)±(3) as Ôcome-alongÕ bene®ts. The same applies to the reductions in pollutants not measured during the short test, because of the short test de®nition (e.g., there is no NOx measurement at idle) or because of the lack of corresponding equipment (e.g., NOx cannot be measured with garage analysers). The estimated emission reductions have been based on the emissions over the certi®cation cycle; however, it is generally recognised that this is not representative of actual driving conditions (Andre et al., 1995). In order to approximate the actual reduction potential, Eij and ERRPi are calculated using the emissions measured over a real world, representative cycle, while vehicles are separated into the groups seen in Fig. 1 according to their emissions over the certi®cation cycle. The methodology requires specifying cut-points and the percentage a. The cut-points are as many as the pollutants measured by the short test, while a is assumed to be one value for all pollutants measured. The eectiveness of each short test depends substantially on the selected cutpoints, which need to take into account all parameters that account for environmental bene®ts, and the costs and drivers' inconvenience resulting from an I/M programme. As Fig. 1 demonstrates, lenient cut-points are associated with low identi®cation rates, cost and inconvenience, but also with low emission reduction. Since most of the vehicles that comply with the emission standards should also pass the short test, errors of commission should be kept to a minimum. Therefore the errors of commission must not exceed 5% of the vehicles tested with the particular short test without any dramatic decrease in the emission reduction potential. Any exemption to the 5% rule should be looked at separately and eventually dealt with speci®c cut-points. Moreover, an I/M programme, apart from being politically and socially acceptable, should not be too costly. This means that the cut-points should be so selected that not more than 20±25% of the vehicles tested fail the test and are sent to maintenance, as indicated by the Environmental Protection Agency (1995). Unlike cut-points, percentage a is not formally stipulated. It is a parameter introduced at the design stage of an I/M programme and it serves only for optimising the eectiveness of the programme. The percentage a separates the needing repair vehicles and those with low bene®t,
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which are treated dierently by the methodology. The estimated emission reduction is based on the needing repair vehicles, while those with low environmental bene®t make no contribution to the estimated reduction with respect to the maintenance eectiveness. a could be a variable accounting for the eectiveness of the maintenance body. Eectiveness is not only related to the performance of local garages, which may vary from one country to another, but also to the fact that some minor failures cannot be detected and appropriate repairs not implemented. It is unrealistic to set a 0% and P4 0%, as this implies that all vehicles above the standard are supposed to receive eective maintenance even though their malfunction may not be detectable. In view of the need to approximate the emission reduction taking into consideration the eect of maintenance, it is suggested that percentage a should not take values below 50%. 3. Special cases Environmental standards, even for a particular vehicle category, may vary with the vehicle production year to re¯ect legislative and technological steps. The methodology, therefore, is restricted to vehicles complying with the same emission standards. An alternative approach to overcome the non-homogenous nature of emission standards could be the normalisation of each vehicle's emissions with the corresponding emission standard. The vertical axis in Fig. 1 becomes non-dimensional and the emission standard for all vehicles is equal to unity. Since each short test should take into consideration the emission standards as well, weighting of the horizontal axis is also required. A common cut-point having no dimensions or expressed in (%)/(g/km) or (ppm)/(g/km), according to the short test, for all vehicles could be determined. The actual cut-point for each vehicle could then be calculated taking into account its emission standard. The current European exhaust emission regulation covering certi®cation of gasoline vehicles involves emission standards for CO and the sum of HC and NOx . This creates a diculty in applying the methodology because the analysis is performed separately for each pollutant. This diculty could be overcome by adequately splitting this standard using the HC over NOx emissions ratio of the measured vehicle emissions. For the determination of the imaginary standards only the emissions of the low polluters is used in order to avoid misleading ®gures due to the malfunctions of high emitters. The same methodology could be applied to short tests having double cut-points, i.e., when an interval is de®ned. For instance, the short test legislated by the European regulations on Roadworthiness of in-use cars (Directive 92/55/EEC), apart from the measurement of CO at idle and high idle, also involves the calculation of the relative air-fuel ratio k, that has an upper and a lower limit 0:97 6 k 6 1:03. The basic chart is thus dierent because there are two areas de®ned as groups 2, 4 and 6 (Fig. 3). In order to evaluate the eectiveness of the short test, ®ve charts are drawn; CO at idle versus certi®cation cycle CO, CO at high idle versus certi®cation cycle CO, k at high idle versus certi®cation cycle CO, k at high idle versus certi®cation cycle HC, k at high idle versus certi®cation cycle NOx . A vehicle needs repair when it belongs to group 6 in any of the charts, while it is an error of commission when it belongs to group 2 but not 6.
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Fig. 3. Modi®ed chart for k.
4. Results The methodology is applied to a sample of three-way catalyst equipped vehicles (Samaras et al., 1998b). The selection of vehicles was based on the relative share of sales of all car manufacturers in Europe and the sample can be considered as being broadly representative. The eectiveness of 10 short tests is evaluated, including steady state tests, unloaded and loaded, and transient tests. The transient short tests include the TUV and Modem short cycles, which were developed especially for the European Commission Short Test Programme (Andre et al., 1998). The short tests, with their abbreviations, are presented in Table 1. The sample consists of approximately 130 Table 1 Short tests and abbreviations Short test Mass emissions in TUV Raw average concentration with lab analysers in TUV Raw average concentration with garage analysers in TUV Mass emissions in modem short Raw average concentration with lab analysers in modem short Raw average concentration with garage analysers in modem short Idle High idle Steady state loaded with garage analysers (50 km/h ± 7 kW) Steady state loaded with lab analysers (50 km/h ± 7 kW)
Abbreviation meTUV ralaTUV ragaTUV meMS ralaMS ragaMS Idle H-Idle ga50-7 la50-7
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vehicles but as Table 2 shows not all of them followed the same test protocol due to technical restrictions (Samaras et al., 1998a). All vehicles were certi®ed against the so-called Euro I emission standards of the European regulation. The emission standards are 3.16 g/km for CO and 1.13 g/km for the sum of HC and NOx (Concawe, 1997). It has been found that HC constitute 53% of the sum of HC and NOx from the low polluters (Samaras et al., 1998a). The percentage a was set equal to 50%. Moreover, the emission reductions were based on a real world cycle (Modem), that was developed in the framework of the EU programme and is aimed at being representative of actual driving conditions (Andre et al., 1998; Samaras et al., 1998b). Table 2 shows the selected cut-points for each short test and the corresponding number of available measurements. In view of the need for an acceptable emission reduction, the cut-points in the transient short tests measuring mass emissions are very close to the corresponding certi®cation standards, in contrast to the cut-points suggested by the Environmental Protection Agency (1995) for IM240 which are 2/3 times higher. This indicates that, on average, European cars are cleaner than their American counterparts. Samaras et al. (1998b) and Calvert et al. (1993) show that in Europe 20% of the vehicles emit 45% of CO and HC (and about 35% of NOx ), while the corresponding numbers in the US suggest that 10% of the vehicles are responsible for as high as half of the pollutants emitted by the vehicle ¯eet. Fig. 4 illustrates how the cut-points are selected for a transient short test measuring mass emissions (meTUV) in terms of CO whilst keeping the HC and NOx cut-points constant. It is made clear that the CO cut-point should not exceed the value of 2 g/km. Lower CO cut-points would lead to high identi®cation rates (P6 ) and high environmental bene®ts (ERRP) but also to errors of commission (P2 ), which would exceed 5% of the tested vehicles. On the contrary, higher CO cut-points would lead to low ERRPs without a signi®cant (if any) decrease in P2 . A sensitivity analysis shows the general pattern of Fig. 4 to be typical for all pollutant cut-points and for all short tests. Fig. 5 presents the parameters characterising the eectiveness of the short tests. These suggest that the transient loaded short tests have the greatest potential in terms of environmental bene®t. The emission reduction potential varies between 15% and 25% for all pollutants, while the steady Table 2 Selected cut-points and corresponding number of measurements Short test meTUV ralaTUV ragaTUV meMS ralaMS ragaMS Idle H-Idle ga50-7 la50-7
Number of measurements
Cut-points CO
HC
NOx
129 74 63 130 78 63 130 130 130 114
2 g/km 0.3% 0.2% 3 g/km 0.3% 0.2% 0.2% 0.2% 0.2% 0.2%
0.3 g/km 1100 ppm C1 500 ppm C1 0.4 g/km 1000 ppm C1 600 ppm C1 900 ppm C1 600 ppm C1 400 ppm C1 600 ppm C1
0.5 g/km 400 ppm ± 0.6 g/km 500 ppm ± ± ± ± 800 ppm
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Fig. 4. Cut-point selection.
Fig. 5. Short tests parameters.
state loaded tests cannot achieve reductions higher than 5%, with the exemption of NOx , at steady state test using laboratory analysers (la50-7). This test was introduced especially for the detection of NOx high emitters because there are no signi®cant NOx emissions under no-load tests. The incorporation of this test aimed only at comparing garage and laboratory analyser performance under steady state loaded tests. Fig. 5 suggests that there is no much dierence as far as the measurement of CO and HC is concerned. The inability of steady state tests to perform well with
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respect to emission reductions is also suggested by Fig. 6, which shows the eectiveness of the short test speci®ed by 92/55/EEC. The total reductions cumulatively achieved by each partial short test of the legislation are also similar to the reductions of the simple unloaded tests of Fig. 5. The dierence in emission reduction potential between the transient and the steady state tests can be explained by the dierence in parameter P6 ± the percentage of very high emitters sent to maintenance. The steady state tests do not have the same ability in identifying high polluters as do the transient tests. A more illustrative parameter that re¯ects this ability would be the IDR of each short test. IDR is not an independent parameter since it can be derived from other parameters: IDR
P6 100% P5 P6
IDR
P4 P6 100% P3 P4 P5 P6
for very high polluters a 50%;
for high polluters a 0%:
IDR values for high and very high polluters are depicted in Fig. 7. Most transient short tests can identify at least 2 out of 3 very high polluters, while steady state tests identify at most one out of ®ve, with the exemption of steady state loaded test using laboratory analysers (la50-7), which is a little more eective. The short test determined by 92/55/EEC identi®es approximately 13% of gross polluters. The IDR for almost all short tests decreases as a decreases because the dispersion is higher around the groups 3 and 4. In contrast, if only the ultra high emitters are targeted (e.g., a 200%), the identi®cation ability of all tests increases. The sample does not contain many such ultra high emitters to allow a thorough analysis but most transient tests seem to have IDR as high as 80% and la50-7 test reaches a value of 40% for a 200%. All other steady state tests do not appear to be capable of detecting even this proportion of such high emitting vehicles.
Fig. 6. Parameters of short test determined by 92/55/EEC.
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Fig. 7. IDR for high (a 0%) and very high (a 50%) polluters.
5. Discussion The methodology provides an algorithm for the evaluation of alternative short tests that could be applied in I/M programmes. This approach takes for granted some conditions which, if not met, could lead to misleading results. Past experience especially in the US, shows that actual emission reductions have been much lower than the predicted (Calvert et al., 1993). One issue is the administrative and institutional arrangements, which in¯uence the organisation of the whole I/M programme. Ineective enforcement of vehicle compliance due to weak registration processes and exemptions, such as repair cost waivers, aect the reliability and eectiveness of the programme (Faiz et al., 1996). A second issue concerns the technical operation of the programme. As far as the inspection procedure is concerned, experiences from the US have shown that improper checks, pre-maintenance and post-maladjustment, are prevalent (Pierson, 1996). The lack of ability of previous I/M programmes to achieve the predicted reductions is, therefore, partly attributed to the inspection procedure itself. Appropriate maintenance has a major role in reducing environmental costs.
Acknowledgements The authors wish to express their sincere thanks to the Directorate Generals VII, XI and XVII of the European Commission for sponsoring the project on which this work is based. Much appreciation goes to all the colleagues of the collaborating institutes and especially to Robert Joumard and Isabelle Vernet of INRETS (France), Dieter Hassel and Franz-Josef Weber of TUV Rheinland (Germany), Rudolf Rijkeboer of TNO (Holland), Tim Barlow of TRL (UK), and Panayotis Pistikopoulos and Theodoros Manikas of LAT (Greece).
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References Andre, M., Hickman, A.J., Hassel, D., Joumard, R., 1995. Driving cycles for emissions measurements under European Conditions, SAE Technical Paper 950926. In: Global Emission Experiences: Processes, Measurements, and Substrates (SP-1094). SAE, Warrendale, pp. 193±205. Andre, M., Hassel, D., Weber, F.J., 1998. The inspection of in-use cars in order to attain minimum emissions of pollutants and optimum energy eciency, Detailed Report 2: Representative European driving cycles for pollutant emissions measurement and short driving cycles for the inspection of in-use cars. Final Report to the European Commission, Thessaloniki, Greece (http://europa.eu.int/comm/dg11/pollutants/inusecars.htm). Calvert, J.G., Heywood, J.B., Sawyer, R.F., Seinfeld, J.H., 1993. Achieving acceptable air quality: some re¯ections on controlling vehicle emissions. Science, 261. Concawe ± The Oil CompaniesÕ European Organisation for Environment, Health and Safety, 1997. Motor vehicle emission regulations and fuel speci®cations ± Part 2. Detailed information and historic review (1970±1996), Report no. 6/97, Brussels. Environmental Protection Agency, 1995. I/M Brie®ng Book ± Everything You Ever Wanted to Know About Inspection and Maintenance. Washington, DC. Faiz, A., Weaver, C., Walsh, M., 1996. Air Pollution from Motor Vehicles- Standards and Technologies for Controlling Emissions. The World Bank, Washington, DC. Pattas, K., Hassiotis, P., 1987. Short test for gasoline powered vehicle emission control. SAE paper 871989, SAE, Warrendale. Pierson, W., 1996. Motor vehicle inspection and maintenance programs ± how eective are they. Atmospheric Environment 30 (21): i±iii. Samaras, Z., 1997, Inspection and maintenance programmes to reduce emissions of in-use cars ± an overview in the European context. International Journal of Vehicle Design 18 (Special issue): 263±279. Samaras, Z., Kitsopanidis, I., Zachariadis, T., Manikas, T., Pistikopoulos, P. (1998a). The inspection of in-use cars in order to attain minimum emissions of pollutants and optimum energy eciency, Detailed Report 5: Short test evaluation. Final Report to the European Commission, Thessaloniki, Greece (http://europa.eu.int/comm/dg11/ pollutants/inusecars.htm). Samaras, Z., Zachariadis, T., Joumard, R., Vernet, I., Hassel, D., Weber, F.-J., Rijkeboer, R., 1998b. Alternative short tests for inspection & maintenance of in-use cars with respect to their emissions performance. International Journal of Vehicle Design 20 (Special issue): 292±303.
www.elsevier.com/locate/trd
Methodology and results of the evaluation of alternative short tests applied in inspection and maintenance programmes Zissis Samaras *, Ioannis Kitsopanidis 1 Laboratory of Applied Thermodynamics, Department of Mechanical Engineering, Aristotle University, 54006 Thessaloniki, Greece
Abstract The aim of this paper is to present a methodology for the evaluation of the eectiveness of alternative short tests that could be applied in an inspection and maintenance programme. The basis for the evaluation, apart from the environmental bene®ts, is the social and political acceptance that constitutes crucial parameters in the implementation of a short test. The methodology has been applied to a large sample of three way catalyst equipped vehicles representative of the European ¯eet and the eectiveness of 10 alternative short tests has been evaluated. The short tests include transient and steady state (both loaded and unloaded) procedures, as well as the idle test of the current European legislation. The steady state tests ®nd it dicult to identify high emitters, approximately 15% are detected, and as a result the predicted potential for environmental bene®t is less than 5% for all pollutants. The transient tests, on the other hand, seem to be able to identify approximately 70% of gross emitters and therefore the emission reduction potential is predicted to be as high as 20% for all pollutants. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Inspection and maintenance; Short test; Emission reduction potential; Errors of commission; Cut-points; Emission standards
1. Introduction The European exhaust emission regulations for the registration of new vehicles have increased in stringency over the last two decades (Concawe, 1997). These legislative steps, that re¯ect the technological achievements over this period, have not proved to be sucient to achieve the aspirated for emission levels of pollutants from vehicles. The sensitivity of the complex electronic systems of modern cars along with the poor maintenance of in-use vehicles seem to be crucial with
*
Corresponding author. Tel.: +30-31-996014; fax: +30-31-996019. E-mail address: [email protected] (Z. Samaras). 1 Present address: Sloan Automotive Lab, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
1361-9209/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 1 3 6 1 - 9 2 0 9 ( 0 0 ) 0 0 0 1 6 - X
112
Z. Samaras, I. Kitsopanidis / Transportation Research Part D 6 (2001) 111±122
regard to the high emission levels from vehicles shortly after their certi®cation. The periodic inspection and repair of in-use vehicles, therefore, have merit. The so-called inspection and maintenance (I/M) programmes aim to ensure that motor vehicle emission control systems are functioning properly throughout the lifetime of the vehicle. Such programmes, that have been enacted for the ®rst time in the 1960s in California, have never achieved the predicted emission reductions (Environmental Protection Agency, 1995; Pierson, 1996). An I/M programme can yield eective results only within an appropriate legislative and administrative framework and when the technical parameters are clearly determined. These technical aspects, that can be grouped by the name Ôshort testsÕ, may contribute substantially to the aim of the emissions reduction programme (Samaras, 1997). The methodology described used here attempts to assess the eectiveness of alternative short tests applied to I/M programmes.
2. Methodology A short test can be considered eective only when it yields an acceptable correlation to the certi®cation cycle or a cycle that is representative of actual driving conditions (Pattas and Hassiotis, 1987; Faiz et al., 1996). Fig. 1 presents such a correlation where the emissions of a particular pollutant over a short test (horizontal axis) are correlated to the corresponding emission levels over the certi®cation cycle (vertical axis). Fig. 1 distinguishes six vehicle groups that play a major role in the analysis, divided by policy lines (Samaras, 1997). The ®rst horizontal line corresponds to the vehicle emission standard for
Fig. 1. Basic chart.
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the target pollutants. The second horizontal line is drawn showing a percentage a above the emission standard and aims to distinguish the high (groups 3 and 4) and the very high polluters (groups 5 and 6) according to their emissions over the certi®cation cycle. The vertical line corresponds to the short test cut-point, i.e., the limit for approving vehicles. This line has been drawn so that the short test is as eective as possible. The vehicles belonging to group 1 are Ôlow pollutersÕ since they emit below the standard and pass the short test. Group 6 vehicles are seen as Ôneeding repairÕ since they are high polluters and fail the short test. The greater the number of vehicles in these two groups, the more eective the short test is. The low polluters of group 2 are incorrectly detected by the short test and, therefore, they are called Ôerrors of commissionÕ. The very high polluters of group 5 are called Ôerrors of omissionÕ, since these vehicles are not detected. In most cases, short tests measure more than one pollutant and this complicates the distribution of vehicles into groups. A particular vehicle could be placed in dierent groups for dierent pollutants. In practice, when a vehicle is tested, only two groups are identi®ed: those passing (groups 1, 3 and 5) and those failing the test (groups 2, 4 and 6). This means that when emissions exceed the cut-point at least in one pollutant the vehicle is sent to maintenance. Thus, a vehicle is referred to: · as needing repair, when at least one pollutant lays in group 6; · as error of commission, when at least one pollutant emission lies in group 2, but none in group 6; · as error of omission, when it passes the short test even though it has excessive emissions at least in one pollutant; and · as low polluter, when it passes the short test and emits below the standard for all pollutants. References to vehicle groups do not, therefore, concern particular pollutants, but are made to pollutants as a whole according to the above de®nitions (Fig. 2). The basic concept for evaluating the eectiveness of alternative short tests is to calculate the overall emission reduction achieved for each pollutant, assuming that vehicles that fail the short test (groups 2, 4 and 6) have the same emission levels as low polluters (group 1). The major contribution to this reduction comes from the vehicles needing repair (group 6), while no emission reduction is achieved by errors of commission (group 2). The vehicles laying in group 4 at least in one pollutant, having though no pollutants in groups 2 and 6 are seen as vehicles oering low environmental bene®t, since their average emissions are low compared to the emissions of the vehicles needing repair. The validity of this assumption depends on the value of a and the emission characteristics of the ¯eet. Assuming the malfunction of these vehicles to be minor, and dicult to detect, the methodology does not take into account the environmental bene®ts from these vehicles. On the other hand, it is assumed that all vehicles needing repair emit after maintenance the same levels of pollutants as when new, i.e., it is assumed that they are completely repaired. This assumption is optimistic and, therefore, the emission reduction should be considered as ÔpotentialÕ. The eect of maintenance is believed to be a parameter independent of the short tests and thus should be investigated separately. If i denotes the pollutants, FC the fuel consumption, and j the vehicle groups, three indexes can be de®ned: Nj , the number of vehicles in group j, Pj , the percentage of vehicles tested laying in group j and Eij , the cumulative pollutant i emissions of group j vehicles measured over the certi®cation cycle.
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Fig. 2. Flowchart for separating the vehicles into groups.
Based on the above, the following `derivative' indexes can be de®ned: Eij ; Emission factor : EFij Nj Emission reduction potential : ERPi EFi6 ÿ EFi1 N6 ; ERPi Emission reduction rate potential : ERRPi 100%: Ei
1 2 3
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The parameters that characterise a short test are: · ERRPi : the potential environmental bene®t that can be achieved with respect to pollutant i, when the particular short test is applied in the framework of an I/M programme. ERRP is the equivalent of the parameter identi®cation rate (IDR) introduced in similar evaluations of the Environmental Protection Agency (1995). · P6 : The part of the vehicle ¯eet sent to maintenance, which generates the above mentioned emission reduction. · P2 : The percentage of vehicles wrongly failed by the short test. Since one objective of an I/M programme is the generation of high environmental bene®t at low cost and with minor inconvenience, ERRPi should be as high as possible with low P6 and P2 values. P6 and P2 should be within the range of political and social acceptance in terms of the costs of maintenance of the programme and legal protection. This does not take into account errors of omission (P5 ), that indirectly indicate a loss of environmental bene®t. Since the environmental gain is directly accounted for by ERRP, P5 provides no additional information. The methodology can be applied to all pollutants for which emission standards exist; i.e., CO, HC and NOx for gasoline vehicles. Direct application of the approach to CO2 emissions and FC is not possible, due to the absence of legal standards. However, the potential reductions of CO2 and FC may be evaluated from Eqs. (1)±(3) as Ôcome-alongÕ bene®ts. The same applies to the reductions in pollutants not measured during the short test, because of the short test de®nition (e.g., there is no NOx measurement at idle) or because of the lack of corresponding equipment (e.g., NOx cannot be measured with garage analysers). The estimated emission reductions have been based on the emissions over the certi®cation cycle; however, it is generally recognised that this is not representative of actual driving conditions (Andre et al., 1995). In order to approximate the actual reduction potential, Eij and ERRPi are calculated using the emissions measured over a real world, representative cycle, while vehicles are separated into the groups seen in Fig. 1 according to their emissions over the certi®cation cycle. The methodology requires specifying cut-points and the percentage a. The cut-points are as many as the pollutants measured by the short test, while a is assumed to be one value for all pollutants measured. The eectiveness of each short test depends substantially on the selected cutpoints, which need to take into account all parameters that account for environmental bene®ts, and the costs and drivers' inconvenience resulting from an I/M programme. As Fig. 1 demonstrates, lenient cut-points are associated with low identi®cation rates, cost and inconvenience, but also with low emission reduction. Since most of the vehicles that comply with the emission standards should also pass the short test, errors of commission should be kept to a minimum. Therefore the errors of commission must not exceed 5% of the vehicles tested with the particular short test without any dramatic decrease in the emission reduction potential. Any exemption to the 5% rule should be looked at separately and eventually dealt with speci®c cut-points. Moreover, an I/M programme, apart from being politically and socially acceptable, should not be too costly. This means that the cut-points should be so selected that not more than 20±25% of the vehicles tested fail the test and are sent to maintenance, as indicated by the Environmental Protection Agency (1995). Unlike cut-points, percentage a is not formally stipulated. It is a parameter introduced at the design stage of an I/M programme and it serves only for optimising the eectiveness of the programme. The percentage a separates the needing repair vehicles and those with low bene®t,
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which are treated dierently by the methodology. The estimated emission reduction is based on the needing repair vehicles, while those with low environmental bene®t make no contribution to the estimated reduction with respect to the maintenance eectiveness. a could be a variable accounting for the eectiveness of the maintenance body. Eectiveness is not only related to the performance of local garages, which may vary from one country to another, but also to the fact that some minor failures cannot be detected and appropriate repairs not implemented. It is unrealistic to set a 0% and P4 0%, as this implies that all vehicles above the standard are supposed to receive eective maintenance even though their malfunction may not be detectable. In view of the need to approximate the emission reduction taking into consideration the eect of maintenance, it is suggested that percentage a should not take values below 50%. 3. Special cases Environmental standards, even for a particular vehicle category, may vary with the vehicle production year to re¯ect legislative and technological steps. The methodology, therefore, is restricted to vehicles complying with the same emission standards. An alternative approach to overcome the non-homogenous nature of emission standards could be the normalisation of each vehicle's emissions with the corresponding emission standard. The vertical axis in Fig. 1 becomes non-dimensional and the emission standard for all vehicles is equal to unity. Since each short test should take into consideration the emission standards as well, weighting of the horizontal axis is also required. A common cut-point having no dimensions or expressed in (%)/(g/km) or (ppm)/(g/km), according to the short test, for all vehicles could be determined. The actual cut-point for each vehicle could then be calculated taking into account its emission standard. The current European exhaust emission regulation covering certi®cation of gasoline vehicles involves emission standards for CO and the sum of HC and NOx . This creates a diculty in applying the methodology because the analysis is performed separately for each pollutant. This diculty could be overcome by adequately splitting this standard using the HC over NOx emissions ratio of the measured vehicle emissions. For the determination of the imaginary standards only the emissions of the low polluters is used in order to avoid misleading ®gures due to the malfunctions of high emitters. The same methodology could be applied to short tests having double cut-points, i.e., when an interval is de®ned. For instance, the short test legislated by the European regulations on Roadworthiness of in-use cars (Directive 92/55/EEC), apart from the measurement of CO at idle and high idle, also involves the calculation of the relative air-fuel ratio k, that has an upper and a lower limit 0:97 6 k 6 1:03. The basic chart is thus dierent because there are two areas de®ned as groups 2, 4 and 6 (Fig. 3). In order to evaluate the eectiveness of the short test, ®ve charts are drawn; CO at idle versus certi®cation cycle CO, CO at high idle versus certi®cation cycle CO, k at high idle versus certi®cation cycle CO, k at high idle versus certi®cation cycle HC, k at high idle versus certi®cation cycle NOx . A vehicle needs repair when it belongs to group 6 in any of the charts, while it is an error of commission when it belongs to group 2 but not 6.
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Fig. 3. Modi®ed chart for k.
4. Results The methodology is applied to a sample of three-way catalyst equipped vehicles (Samaras et al., 1998b). The selection of vehicles was based on the relative share of sales of all car manufacturers in Europe and the sample can be considered as being broadly representative. The eectiveness of 10 short tests is evaluated, including steady state tests, unloaded and loaded, and transient tests. The transient short tests include the TUV and Modem short cycles, which were developed especially for the European Commission Short Test Programme (Andre et al., 1998). The short tests, with their abbreviations, are presented in Table 1. The sample consists of approximately 130 Table 1 Short tests and abbreviations Short test Mass emissions in TUV Raw average concentration with lab analysers in TUV Raw average concentration with garage analysers in TUV Mass emissions in modem short Raw average concentration with lab analysers in modem short Raw average concentration with garage analysers in modem short Idle High idle Steady state loaded with garage analysers (50 km/h ± 7 kW) Steady state loaded with lab analysers (50 km/h ± 7 kW)
Abbreviation meTUV ralaTUV ragaTUV meMS ralaMS ragaMS Idle H-Idle ga50-7 la50-7
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vehicles but as Table 2 shows not all of them followed the same test protocol due to technical restrictions (Samaras et al., 1998a). All vehicles were certi®ed against the so-called Euro I emission standards of the European regulation. The emission standards are 3.16 g/km for CO and 1.13 g/km for the sum of HC and NOx (Concawe, 1997). It has been found that HC constitute 53% of the sum of HC and NOx from the low polluters (Samaras et al., 1998a). The percentage a was set equal to 50%. Moreover, the emission reductions were based on a real world cycle (Modem), that was developed in the framework of the EU programme and is aimed at being representative of actual driving conditions (Andre et al., 1998; Samaras et al., 1998b). Table 2 shows the selected cut-points for each short test and the corresponding number of available measurements. In view of the need for an acceptable emission reduction, the cut-points in the transient short tests measuring mass emissions are very close to the corresponding certi®cation standards, in contrast to the cut-points suggested by the Environmental Protection Agency (1995) for IM240 which are 2/3 times higher. This indicates that, on average, European cars are cleaner than their American counterparts. Samaras et al. (1998b) and Calvert et al. (1993) show that in Europe 20% of the vehicles emit 45% of CO and HC (and about 35% of NOx ), while the corresponding numbers in the US suggest that 10% of the vehicles are responsible for as high as half of the pollutants emitted by the vehicle ¯eet. Fig. 4 illustrates how the cut-points are selected for a transient short test measuring mass emissions (meTUV) in terms of CO whilst keeping the HC and NOx cut-points constant. It is made clear that the CO cut-point should not exceed the value of 2 g/km. Lower CO cut-points would lead to high identi®cation rates (P6 ) and high environmental bene®ts (ERRP) but also to errors of commission (P2 ), which would exceed 5% of the tested vehicles. On the contrary, higher CO cut-points would lead to low ERRPs without a signi®cant (if any) decrease in P2 . A sensitivity analysis shows the general pattern of Fig. 4 to be typical for all pollutant cut-points and for all short tests. Fig. 5 presents the parameters characterising the eectiveness of the short tests. These suggest that the transient loaded short tests have the greatest potential in terms of environmental bene®t. The emission reduction potential varies between 15% and 25% for all pollutants, while the steady Table 2 Selected cut-points and corresponding number of measurements Short test meTUV ralaTUV ragaTUV meMS ralaMS ragaMS Idle H-Idle ga50-7 la50-7
Number of measurements
Cut-points CO
HC
NOx
129 74 63 130 78 63 130 130 130 114
2 g/km 0.3% 0.2% 3 g/km 0.3% 0.2% 0.2% 0.2% 0.2% 0.2%
0.3 g/km 1100 ppm C1 500 ppm C1 0.4 g/km 1000 ppm C1 600 ppm C1 900 ppm C1 600 ppm C1 400 ppm C1 600 ppm C1
0.5 g/km 400 ppm ± 0.6 g/km 500 ppm ± ± ± ± 800 ppm
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Fig. 4. Cut-point selection.
Fig. 5. Short tests parameters.
state loaded tests cannot achieve reductions higher than 5%, with the exemption of NOx , at steady state test using laboratory analysers (la50-7). This test was introduced especially for the detection of NOx high emitters because there are no signi®cant NOx emissions under no-load tests. The incorporation of this test aimed only at comparing garage and laboratory analyser performance under steady state loaded tests. Fig. 5 suggests that there is no much dierence as far as the measurement of CO and HC is concerned. The inability of steady state tests to perform well with
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respect to emission reductions is also suggested by Fig. 6, which shows the eectiveness of the short test speci®ed by 92/55/EEC. The total reductions cumulatively achieved by each partial short test of the legislation are also similar to the reductions of the simple unloaded tests of Fig. 5. The dierence in emission reduction potential between the transient and the steady state tests can be explained by the dierence in parameter P6 ± the percentage of very high emitters sent to maintenance. The steady state tests do not have the same ability in identifying high polluters as do the transient tests. A more illustrative parameter that re¯ects this ability would be the IDR of each short test. IDR is not an independent parameter since it can be derived from other parameters: IDR
P6 100% P5 P6
IDR
P4 P6 100% P3 P4 P5 P6
for very high polluters a 50%;
for high polluters a 0%:
IDR values for high and very high polluters are depicted in Fig. 7. Most transient short tests can identify at least 2 out of 3 very high polluters, while steady state tests identify at most one out of ®ve, with the exemption of steady state loaded test using laboratory analysers (la50-7), which is a little more eective. The short test determined by 92/55/EEC identi®es approximately 13% of gross polluters. The IDR for almost all short tests decreases as a decreases because the dispersion is higher around the groups 3 and 4. In contrast, if only the ultra high emitters are targeted (e.g., a 200%), the identi®cation ability of all tests increases. The sample does not contain many such ultra high emitters to allow a thorough analysis but most transient tests seem to have IDR as high as 80% and la50-7 test reaches a value of 40% for a 200%. All other steady state tests do not appear to be capable of detecting even this proportion of such high emitting vehicles.
Fig. 6. Parameters of short test determined by 92/55/EEC.
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Fig. 7. IDR for high (a 0%) and very high (a 50%) polluters.
5. Discussion The methodology provides an algorithm for the evaluation of alternative short tests that could be applied in I/M programmes. This approach takes for granted some conditions which, if not met, could lead to misleading results. Past experience especially in the US, shows that actual emission reductions have been much lower than the predicted (Calvert et al., 1993). One issue is the administrative and institutional arrangements, which in¯uence the organisation of the whole I/M programme. Ineective enforcement of vehicle compliance due to weak registration processes and exemptions, such as repair cost waivers, aect the reliability and eectiveness of the programme (Faiz et al., 1996). A second issue concerns the technical operation of the programme. As far as the inspection procedure is concerned, experiences from the US have shown that improper checks, pre-maintenance and post-maladjustment, are prevalent (Pierson, 1996). The lack of ability of previous I/M programmes to achieve the predicted reductions is, therefore, partly attributed to the inspection procedure itself. Appropriate maintenance has a major role in reducing environmental costs.
Acknowledgements The authors wish to express their sincere thanks to the Directorate Generals VII, XI and XVII of the European Commission for sponsoring the project on which this work is based. Much appreciation goes to all the colleagues of the collaborating institutes and especially to Robert Joumard and Isabelle Vernet of INRETS (France), Dieter Hassel and Franz-Josef Weber of TUV Rheinland (Germany), Rudolf Rijkeboer of TNO (Holland), Tim Barlow of TRL (UK), and Panayotis Pistikopoulos and Theodoros Manikas of LAT (Greece).
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